Will, I have an 1861 Navy Colt Conversion, which is a 2nd. Generation Colt, converted by R&D. It is exceptional, and from a quality standpoint, nothing else compares. If you don't mind a pretty hefty wait, then have them do the work. If you have found one that someone has, (already converted) then BUY IT.
With all of that said, the Uberti products are of very good quality.....they are not like a Kenny Howell 2nd. Generation Colt, but they ain't shabby either. I also have a Uberti Open Top and a Uberti Richards-Mason 1860 (both in .44), and I've got a handful of other conversions that are of different makes....
So, both options you have mentioned are good, and the R&D is worth the extra money. It all depends on if you wish to wait or not.....